Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
The circular optical modes in monolithic resonators are referred to as “whispering gallery modes” (WGM) or “morphology dependent resonances” (MDR). such modes or resonances are closed trajectories of light (standing light waves) supported by total internal reflections from the boundaries of a resonator. A WGM occurs when standing light waves of a particular emission profile are confined by a near-total internal reflection inside the surface of a spherical dielectric cavity (Moller et al, Applied Physics Letters 83(13):2686-2688, 2003).
The WGM technology is described in detail in International Patent Publication No. WO 2005/116615, which is incorporated herein by reference. WGM technology is predicated, in part, on the phenomenon that fluorophores enable a distinctive WGM profile to be generated. The fluorophores are incorporated onto quantum dots which are into the microparticles by diffusion or may be incorporated during their manufacture. The type of fluorophore is unlimited and may for example be an organic dye, a rare earth based lumophore, a semiconductor nanocrystal of various morphologies and compositions. a phosphor or other material which emits light when illuminated. This fluorophore or mixture thereof is then attached to microspheroidal particles. When a target analyte interacts with a binding partner immobilized to the microspheroidal particle, the WGM profile changes, enabling detection of the binding event.
WGM allow only certain wavelengths of light to be emitted from the particle. The result of this phenomenon is that the usual broad emission (10-100 nm wide) bands from, for example, a fluorophore, become constrained and appear as a series of sharp peaks corresponding effectively to standing mode patterns of light within the particle. The WGM profile is extremely sensitive to changes at the surface of the microspheroidal particle and the WGM profile changes when the microspheroidal particle interacts with analytes or molecules within its environment.
The detection of rare analytes in samples of diverse origin requires a sensitive, versatile and practical detection means. There is a necessity to devise methods to increase sensitivity, versatility and practicality of WGM for the detection of analytes.